Override #page.hfeed.site to make content appear not opaque (12 posts)

So I have my page set up mostly how I want (the main page anyway) - I figured out how to give the main content area and wrapper a cool opaque look. I did this with the #page.hfeed.site selector. I like the way that this looks for the most part but I would like to remove the opacity from the content of the actual posts if I can. I am wondering if there is a selector that I can use to over ride the settings for that portion of the page - I have tried .entry-content img, #content, #content-entry and nothing seems to work. I tried to make each individual part of the page opaque but I didn't have much success - #page.hfeed.site seems to be the only one that makes it look (almost) how I want.
this is a page you can look at: http://www.daily-mash.com/wordpress2/category/photos/

Actually if there is a way that I can make just the images that I post not opaque that would be ideal.

on a side note - does anyone know of a good place that has a list of all the selectors and what they actually apply to? I can't seem to find a good place for this - thank you in advance for your help! Appreciate it!

..a good place that has a list of all the selectors and what they actually apply to?

There is no need for the list and the list will never happen because each site is different. What we need is the tool to figure it out, it's available for most modern user under F12. Lots of folk use Firebug extension of Firefox.

for some reason none of the ones that I use the . with make any changes. I have been using the web developer tool in Chrome to help identify which selector to use for which portion of the site but I haven't had much luck with those . ones - even when chrome displays them that way

So I figured out how to make the content part non-opaque - the problem is that when I add in the #page.hfeed.site or div#main-wrapper selectors - they take presidence over the #div.entry-content that I have set up - is there a way to define which rules take priority over the others?? Thanks for the help!